In The Journal of Domestic Appliances and Sewing Machine Gazette of 1887 you will find an advert from John Tester of London, advertising as the agent for the new patent Pickering, Son & Norton's ACME Door Check and Spring.
https://archive.org/stream/journaldomes151887lond#page/n15/mode/2up/search/pickering+and+norton+acme
http://discovery.nationalarchives.gov.uk/details/rd/08e63fb9-441c-47b5-a987-6e51f5fc6d93
This is so far the only floor spring I have come across that has this split brass cover arrangement.